Magnetron generator



Dec. 25, 1951' .F. LUDI MAGNETRON GENERATOR 2 SI-iEETS-SHEET 1' Filed March 9, 1943 Dec. 25, 1951 F. LUD] 2,579,593

MAGNETRON GENERATOR Filed March 9, 1945 2 SHEETS-SHEET 2 Patented Dec. 25, 1951 MAGNETRON GENERATOR Fritz Liidi,

"Patelhold Baden, Switzerland; assignor to Patentverwertungs- & Elccktro- Holding A.-G., Glarus, Switzerland Application March 9, 1943, Serial No. 478,533 In Switzerland February 9, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires February 9, 1962 15 Claims. 1

This invention relates, generally, to oscillation generators and it has particular relation to de-' vices for generating ultra high frequency electromagnetic waves.

The object of the present invention is to avoid certain disadvantages of the prior ultra high frequency generators whilst at the same time making use of the advantages which are offered by combining the means for the self-excitation of the oscillations at maximum eiiiciency with a hollow resonator which alone determines the oscillation frequency. The invention thus concerns a magnetron for producing ultra-short electro-magnetic waves and which is characterised by the provision for the oscillation system of a practically closed annular hollow body bounded in a radial direction by two cylindrical casings, the cylindrical casing nearer to the axis being divided into two parts by a zigzag slot which is closed in the tangential direction, said parts being at diiierent alternating potential but at the same direct potential relative to the cathode located in the axis of the system.

An important fact as regards the present invention is that in a hollow resonator an electrical oscillation is excited by which in a known manner a continuous conversion of capacity energy into inductive energy occurs. There is a so-called magnetic dipolar excitation of the cavity whereby the latter is able to deliver energy in the form of electro-magnetic oscillations.

A number of constructional examples of the invention are illustrated in the accompanying drawings in which:

Fig. 1 is a perspective view of a hollow resonator element embodying the invention,

Fig. 2 is a schematic axial section through the electrode assembly of a magnetron embodying the invention,

Fig. 3 is a schematic axial section through another form of electrode assembly,

Fig. 4 is an axial section through an all-metal magnetron tube construction in which the resonator element constitutes the vacuum vessel or tube,

Fig. 5 is an axial section,,similar to that of Fig. 4, and showing a permanent magnet and variable means therefor, and

Fig. 6 is a perspective view of a resonator chamber within an evacuated glass envelope.

The resonator element as shown in Fig. 1 is in tended for use in a magnetron for generating ultra-short electro-magnetic waves. The zigzagshaped slot Z produces in the inner cylinder the interpenetrating segments S1 and 8;. These segments are laminations together with the outer cylinder and the radial side Walls form the hollow body H which acts as a hollow resonator, the seg ments mutually representing the capacity and the remaining part of the hollow body the inductance of the latter. When the hollow resonator oscillates the laminations S1 are positive and the segments S2 negative at a certain instant. As a result of the oscillating process these charges now change places so that after a half cycle the segments S1 become negative and the laminations S2 positive. For this change-over the hollow body H, which acts as an inductance, is used as the inductive connection. 1

The more complete illustration of the electrode assembly of Fig. 2 difiers from Fig. 1 in so far as a cathode K surrounded by a grid G is also shown, also that an output loop L for extracting the highfrequency energy is provided and finally perpen dicularly to the axis of the magnetron metal plates P1 and P2 are arranged for preventing the radiation of high frequency energy. The capacity of the oscillation circuit is again formed by the adjoining segments S1, S2 whilst the inductance is formed by that part of the hollow body H comprising the end surfaces and the outer cylinder.

The pole pieces E of a generally C-shaped magnet are positioned close to the side walls of the reso nator chamber H. the pole pieces preferably having openings therethrough for the leads to the cathode K and grid G. Field windings W on the pole pieces E are energized from a direct current source, not shown, to establish a unidirectional magnetic field within the resonator chamber.

The frequency of the generated oscillations depends upon the volume of the resonator chamber and arrangements for varying the volume will be described later. A Lecher line for extracting energy from the resonator chamber also has an influence upon the frequency of the resonator oscillations, and it is thus possible to ,eifect a frequency modulation by connecting a' Lecher line. L: across a pair of electrodes S1, S2, the Lecher line being closed by a variable capacity J. a i

Fig. 3 illustrates a further embodiment of the invention developed from the construction illustrated in Fig. 2. The cathode K is smaller and located in the immediate vicinity of the side plate P2. The side plate P1 can be used as a control grid if it is insulated from the remaining parts of the device. This construction is particularly suitable for avoiding the reheating effect of the cathode. A Lecher wire L1 that is closed by a sliding bar K may be connected to an adjacent pair of the inner wall segments 51, S2 for extractstruction of this kind. The same referencel etters are used for the same elements as in the previousfigures. The generator is cooled". by liquid cir culated through pipes R which are positioned ad jacent or secured to the side walls of the chamber. H in line with the ends of the segments-.81, S2...

The volume of the chamber may be varied by an ing energy from the resonator. The volume of the 7 adjustable piston M. Side walls are used here:

instead of side plates for protection against radiatlon... The plates; P41 located parallel, to; the side walls inside-- the cathode spaceserve as a. screen.

inside. the; inner; cylinder; f orthe: electrical field which. occurs; due. to the. anode; potential at, the said: walls,, thus: preventing any, undesirable deviation of the electrons.

The:'construction.- according. to the invention possesses several advantages- It has complete electrical symmetry as regards each segment pair sincea-ll segments, are of'thesamedimensions and areauni formly spaced.circumferentially. Due to. lieati-beingconducted'tothezside Walls the thermal loading of; the anodeis reduced. Theall-metal construction illustrated in Fig. 45- is suitable for large: powers because byconstructing theresonator: as a: vacuum: vessel; it. is possible. to obtain azready' removal of heat from the anode. The wave; length. of the oscillation is determined by the mutual: capacitance-ofthe segments and the diameter oi-thehollow resonator. For the same wavelengths; the: dimensions of the generator ac:- cordingtov the invention: are larger thanth'ose: of the known kinds of.:magnetrons.. Particularly the actual external diameter ofthe anodeis-three to. four times larger and. this enables a better: are rangement-i of the cathodesandicontrol:grids; even for: small wave: lengths; Thelarger-radial dimen' sion enables a spiral cathode to be used for high currents. Furthermore the axial dimension or length of the cavity resonator is less than the diameter and can be reduced. to. a. minimum so thatathe pole shoesof the magnet 'needrnot be so my apartand therefore permanentzma-gnets can be. used. Since the-wavelength is determined; by the mutual capacitance of the segments-and the diameterof; the hollow" resonator: this. value. is definitely'fixedafon-a particularcase. This is a considerable advantage; when compared: with" a lmownconstruction where; the wave length isnot clearly-defined;

As showniin Fig; 5, theside walls and the-cylindrical walls of-the resonator. chamber'I-I maybe made ofdifferent materials; for examplethe inner slotted cylindrical surface S1, S2 canbemade: of special heat resisting' material, for instance tantalum; because this issubjected' to a strong heating actiondue' to the impactof the electrons. The permanent magnet M" is'made in two sections that-may be separated'for the introduction of the resonator chamber H between the pole pieces. The strength of the magnetic fieldmay be, varied bya magnetic shunt or'by-a screw 1 that-adjusts a magnetic plug 2' into and out of a slot in the magnet te. vary" the reluctance of the magnetic path. The cathode K may be of the large surface type, as illustrated.

As shown in Fig. 6, a resonator chamber may be mounted within a glass envelope GI by means of metal vanes F-that areasoldered orwelded to the chamber and the lead-in wires. Theinner wall segments S1, S2 are separate strips or rods that are welded to the side Walls of the chamber H.

Theshape-of the hollow body H can diiler from that shown in Fig. l by bevelling the sharp edges or. providing the side-surfaces with recesses. The

interpenetrating segments formed as a result of the" zigzag slot can be made so narrow and thick that-they finally-become rods. The segments can beeithersoldered to the side walls of the hollow resonator, fitted into the resonator, as shown in Figs; 5 and 6;, or fixed in any other suitable manner.

Thercathode K is heated either directly or indirectly. Generally there is suificient space to enable. a. large surface cathode. tobe used see Fig. 5.- I The allrmetal. construction is the, most. favoun. able as regards cooling, because, it. provides. a maximum of. metal surface, Generally both liquid. andv air. cooling are employed,.particu1ar care being taken that. the inner cylinder can readily. getrid of its heatby. meansofagood. and rapid conduction away from. the side wall where the segments end.

Inorder to obtain. full useoi the magnet it. is advisable to provide holes in its. pole shoes M2. into Whichthe. insulatorsv (Fig. 5.)'. lying in. the axis 01" the magnetron. can be, fitted exactly. and

through which also-the leadstothe cathode can pass. .By thismeans thepoles-are as. nearto each other. as possiblev and the magnetic field therefore attains. its. maximum, value. In. order to. insert the magnetron. between the poles these. mustbe moved. apart and. then pushed. together again. This can for, instance. be achievedby making the magnetintwo parts which can be fittedtogether.

By varying the volume of the magnetron. at. the places. where the electricor magnetic fieldexists it is possible to obtain a variation in the fre quency of the. generator.oscillations;v thatis to say by this means it is possible to modulate its frequency. Therefore for instance by meansiof the described elastic deformation of the walls at the pointswhere there is. maximum electrical or magnetic energy, it is. possible to. obtain afre quency modulation... In. the, constructional ex ample-shown in Fig. 4 the strongest electrical field is in the vicinity of the axis whilst themaximum value, of the magnetic field is in the neighborhood of the outer cylindrical envelope. The volume can also be varied by. introducing a metal rodor piston into the inside of'the resonator.

The maximum power setting of the magnetron must, be adjusted by. varying the. magnetic field and by a corresponding voltage variation. If, a permanent magnet is used it is possible. to adjust the strengthof the magnetic field. by a variable interruption, of the; magnetic flux. One way of varying the field strength in the magnetron is by suitably displacinga ferromagnetic body. 2, Fig, sothat a variable number of lines of force are short-circuited.

I claim: I

1. A magnetron, comprisinga cavity resonator having a. cathode'in the interior thereof positioned. atj'ri ht gle to. two. par llel. suriaces. dc.- fining the. shortest dimension of said. resonator, an. anodestructure surrounding saidcathode, and composed. of a multiplicity oiequallength anode segments greater than two located between said surfaces and mounted with alternate segments on the same surface and adjacent segments on opposite ones of said two surfaces of said cavity resonator, and means adjacent said resonator for producing a magnetic field having flux lines extending in a direction substantially parallel to said cathode.

2. A magnetron comprising a cylindrical cavity resonator whose length is short relative to its diameter, a cathode within said resonator, and an anode structure surrounding said cathode, said anode structure being composed of an even number of equal length anode segments greater than two located between those surfaces of said resonator which define the boundaries of said length and mounted in the interior with alternate segments on opposite faces of said cavity resonator, and means adjacent said resonator for producing a magnetic field.

3. A magnetron comprising a cylindrical cavity resonator whose length is short relative-to its diameter, a cathode in the center and positioned along the length of said cavity resonator, and an anode structure surrounding said cathode and which is composed of a plurality of identically dimensioned anode segments greater than two mounted in the interior, alternate segments being mounted on opposite faces of said cavity resonator, and means adjacent said resonator for producing a magnetic field having flux lines extending in a direction substantially parallel to said cathode.

4. A magnetron comprising a cavity resonator whose length is short relative to its transverse dimensions, a cathode in the interior and posi-v tioned along the length of said cavity resonator and located between opposite faces thereof, and an anode structure surrounding said cathode and composed of an even numbered multiplicity of equal dimensioned anode segments greater than two, alternate segments being directly connected the interior of said resonator and located between said flat surfaces, said anode structure being composed of a plurality of equal dimensioned anode segments greater than two, alternate segments being directly connected to the same surface and adjacent segments being directly connected to the opposite surfaces of the resonator, and means located externally of said resonator for producing a magnetic field with flux lines parallel to said cathode.

8. An electron discharge device comprising. a cavity resonator having a pair of fiat surfaces defining its shortest dimension, a cathode and an anode in the interior of said resonator and located between said fiat surfaces, said anode structure being composed of a plurality of equal dimensioned anode segments greater than two, alternate segments being directly connected to the same surface and adjacent segments being directly connected to opposite surfaces of the resonator.

9. An anode assembly for a magnetron comprising a cavity resonator having annular conductive end walls and bounded in a radial direction by cylindrical conductive walls, the inner cylindrical wall being divided into a plurality of pairs of anode segments by a zig-zag slot, whereby adjacent anode segments are connected to and supported by opposite annular end walls, the'axial length of said cavity resonator being short relative to the diameter of the outer cylindrical wall and the natural resonant frequency of the cavity resonator being determined by the capacitance between said anode segments and its relation to the inductance provided by said outer cylindrical wall and the annular end walls connecting the same to said anode segments, cathode means of more than filamentary diameter located within the cylindrical space defined by said anode segments and with the axis thereof parallel to said anode segments, insulating bushings closing the axial openings in said end walls and supporting I said cathode means, and pipes adjacent the ends to the same face and adjacent segments being connected to opposite faces of the resonator, and magnetic pole pieces at opposite ends of said cathode for producing a magnetic field.

5. An electron discharge device comprising an evacuated cavity resonator having a short dimension and a long dimension, a cathode in its interior and an anode structure coaxial with said cathode, said resonator having two substantially parallel surfaces defining said short dimension, said cathode and anode being positioned between said two surfaces, said anode comprising a multiplicity of identically dimensioned anode segments greater than two mounted with alternate 0 segments on the same side and adjacent segments on opposite sides of said cavity resonator.

6. A magnetron comprising a cavity resonator having two substantially parallel flat surfaces, a cathode in the interior of said resonator at right angles to said fiat surfaces, and an anode structure surrounding said cathode and coaxial therewith, said anode structure having a multiplicity of identically dimensioned anode segments greater than two mounted with alternate segments on the same surface and adjacent segments on difi'erent ones of said two fiat surfaces, said cathode including a hollow electron emitting element having a heater therein, and shields at the ends of said cathode for confining the electrons emitted by said cathode.

7. A magnetron comprising a cavity resonator having a pair of fiat surfaces defining its shortest dimension, a cathode and an anode structure in of said anode segments for the circulation of a cooling medium therethrough to cool said anode segments.

10. An anode assembly for a magnetron comprising a cavity resonator having annular conductive end walls and bounded in a radial direction by cylindrical conductive walls, the inner cylindrical wall being divided into a plurality of pairs of anode segments by a zig-zag slot, whereby adjacent anode segments are connected to and supported by opposite annular end walls, the axial length of said cavity resonator being short relative to the diameter of the outer cylindrical wall and the natural resonant frequency of the cavity resonator being determined by the capacitance between said anode segments and its relation to the inductance provided by said outer cylindrical wall and the annular end walls connecting the same to said anode segments, cathode means of more than filamentary diameter located within the cylindrical space defined by said anode segments and with the axis thereof parallel to said anode segments, insulating bushings closing the axial openings in said end walls, an insulated bushing supported by the outer cylindrical wall, and output means within the annular interior of said cavity resonator and having a lead extending through said last mentioned insulator bushing.

ll. An electrode assembly as recited in claim 10, wherein the outer walls of said cavity resonator and said insulating bushings form. the evacuated envelope of the magnetron.

amazes 12. A magnetron for generating ultra-short electro-magnetic waves comprising an annular hollow conductive body constituting a cavity resonator with annular end walls and bounded in a radial direction by two cylindrical walls, the inner cylindrical Wall being divided into two parts by a zig-zag slot providing a plurality of pairs of interfitting anode segments supported in alternation on said end walls, the geometry of said cavity resonator being such that the natural resonant frequency is determined by the mutual capacitance of the interleaved anode segments and its relation to the inductance provided by said outer cylindrical wall and the end walls connecting the same to said anode segments, said annular end, walls extending inwardly from said inner cylindrical wall to constitute parts of a sealed envelope for said magnetron, a magnet located outside of and adjacent said cavity resonator and having spaced pole pieces at opposite end'sof the space defined by said inner cylindrical wall to establish a unidirectional magnetic field within said space and parallel to the axis thereof, and a cathode extending through said space parallel to the magnetic field, said pole pieces having openings therethrough in which leads to the cathode are arranged.

hollow conductive body constituting a cavity resonator with annular end walls and bounded in a radial direction by two cylindrical walls, the inner cylindrical wall being divided into two parts by a 'zig-zag, slot providing a plurality of pairs of interfitting anode segments supported in alternation on said end walls, the geometry of said cavity resonator being such that the natural resonant frequency is determined by the mutual capacitance of the interleaved anode segments and its relation to the inductance provided by said outer cylindrical wall and the end walls connecting the same to said anode segments'means positioned outside of and adjacent said cavity resonator to establish a unidirectional magnetic field within the space defined by said inner cylindrical wall and parallel to the axis thereof, and a cathode extending through said space parallel to themagneticfield; the end walls of the hollow body extending inwardly from said inner cylindrical wall to. confine electrons emitted by said cathode to said space defined by said inner cylindrical wall. 14-. A magnetronv as recited in claim 13, in combination with insulating bushings supporting said cathode and mounted in relatively small openings in said extended end walls. 15. A magnetron as recited in claim. 14, in combination with plates within the space defined by said inner cylindrical wall and immediately adjacent said. extended end walls, said plates being insulated from. said extended end walls and adapted to be maintained at a direct current potential of the order of the cathode potential.

- FRITZ LUDI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,071,311 Linder Feb. 16, 1937 2,115,521 Fritz et al Apr. 26, 1938 2,144,222 Hollmann Jan. 17, 1939 2,147,143 Braden Feb. 14, 1939 2,147,159 Gutton et al Feb. 14, 1939 2,151,766 Hollmann Mar. 28, 1939 2,154,758 Dallenbach Apr. 18, 1939 2,167,201 Dallenbach July 25, 1939 2,233,261 Hollmann Feb. 25, 1941 2,238,272 Linder Apr. 15, 1941 2,289,220 Smith July 7, 1942 2,409,222 Morton Oct. 15, 1946 FOREIGN PATENTS Number Country Date 509,102 Great Britain Oct, 7, 1938 215,602 Switzerland Oct. 1, 1941 215,600 Switzerland c Oct. 16, 1941 509,102

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